RAD Studio
Displaying and Editing a Subset of Data Using Filters

An application is frequently interested in only a subset of records from a dataset. For example, you may be interested in retrieving or viewing only those records for companies based in California in your customer database, or you may want to find a record that contains a particular set of field values. In each case, you can use filters to restrict an application's access to a subset of all records in the dataset. 

With unidirectional datasets, you can only limit the records in the dataset by using a query that restricts the records in the dataset. With other TDataSet descendants, however, you can define a subset of the data that has already been fetched. To restrict an application's access to a subset of all records in the dataset, you can use filters. 

A filter specifies conditions a record must meet to be displayed. Filter conditions can be stipulated in a dataset's Filter property or coded into its OnFilterRecord event handler. Filter conditions are based on the values in any specified number of fields in a dataset, regardless of whether those fields are indexed. For example, to view only those records for companies based in California, a simple filter might require that records contain a value in the State field of "CA".

Note: Filters are applied to every record retrieved in a dataset. When you want to filter large volumes of data, it may be more efficient to use a query to restrict record retrieval, or to set a range on an indexed table rather than using filters.
The following topics describe how to work with filters:

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